Electron discharge device



United States Patent 3,195,003 ELECTRON DESCHARGE DEVHCE Ante-n van der.lagt, Wheeler Township, Steuben County, N.Y., assigrror to WestinghouseEiectric Corporation, Pittsburgh, Pa, a corporation of PennsylvaniaFiled Nov. 16, 1962, er. No. 238,229 Ciaims. (Cl. 313-337) The presentinvention relates to electron discharge devices and more particularly toelectron emissive cathodes of the thermionic type for use in electrondischarge devices.

it is known in the art of thermionic cathodes for electron dischargedevices that the rate of electron emission for a given material isprimarily dependent upon two factors: namely, the area and thetemperature of the emissive surface. The most common form of indirectlyheated emissive cathode comprises a long sleeve or tubular member ofsuitable cross-sectional configuration having a heating element disposedWithin the tubular member. An electron emissive coating is placed on theoutside of the tubular member. This type of cathode provides a largeemissive area and is also efiicient in that, as the heater is in veryclose proximity to the emissive surface, the heat transfer to thetubular member is good. Also, as the openings in the ends of the tubularmembers are small and relatively distant with respect to the majority ofthe length of the heater, only small amounts of the heat produced by theheater are lost through these openings. Also, the heat losses due toconduction to the support members (usually mica-s), cathode tab andheater legs are small when compared to the total heat capacity of theheater.

While cathodes of the above-described nature have proven generallysatisfactory for a great number of devices, they do suffer from certaindefects. Among these defects is the fact that the long cathode isparticularly susceptible to microphonic noises due to actual physicalvibration and, therefore, the support of the cathode within an electrondischarge device can present some serious problems. Also, the longcathode structure necess'itates a correspondingly long device which maybe undesirable in certain circumstances.

These deficiencies in the so-called long cathode may be overcome throughthe use of 'a shorter cathode having a larger cross sectional area.However, prior attempts at a short cathode have largely beenunsatisfactory in that due to the relatively large open ends of thetubular section and the relatively short distance from these open endsto most parts of the heater, radiation losses have been extremely high.Also, the thermal conduction losses to the support members increasesrapidly with the increase in tube diameter. While it is true that, evenincluding these losses, the cathode may be brought to the propertemperature by increasing the heater wattage and hence the temperatureof the heater, this results in a lowering of the overall efiiciency ofthe device. Increased heater temperature may also be extremelydetrimental to the heater itself as, by virtue of the highertemperature, the heater will have a greatly shortened life. It is,therefore, an object of this invention to provide an improved electrondischarge device.

Another object is to provide an improved thermionic electron emissivecathode.

A further object is to provide a thermionic cathode of high efficiency.

Another object is to provide a thermionic cathode in which the ratio oflength to width is small.

A still further object is to provide an electron emissive cathode ofhigh electron emission and low heater temperature.

Stated briefly, the present 'inve'ntion'describes an electron dischargedevice employing a double wall cathode structure of short length andlarge cross sectional area. The double wall structure is preferablycomprised of two -tubular members of different cross sectional areaswhich are coaxially aligned and which have the spacing between the two-m'er'nbers at one end thereof closed off. A cathode shield, which iscommon in many electron discharge devices, is positioned at the otherend of the tubular members and serves to etfectively close oif that endof the tubes. The heater assembly for the device is located in thespacing between the two tubular members.

Further objects and advantages of the invention will become apparent asthe following description proceeds and features of novelty 'whichcharacterize the invention will be pointed out in particularity in theclaims annexed to and forming a partof this specification.

For a better understanding of the invention, reference may be had to theaccompanying drawings, in which:

FIGURE 1 is an 'elevation'al view, partially broken away and partiallyin section of a discharge device embodying the cathode of the presentinvention in its preferred form; and I FIGS. 2 and 3 are modificationsof the cathode of FIG.'1 in accordance with the present invention.

With reference to FIG. 1, there is shown a discharge deviceincorporating the invention in its preferred form. The device includesanenvelope '10 which is closed at one end and is provided with atipped-off exhaust tube 12. The other end of the envelope 10 is closedoff with a button stem header 14. 'Disposed within the envelope 1% is anelectrode cage assembly indicated generally at 16. The cage assemblyincludes an anode 18, a grid 20, and a cathode 22. The cage assembly issupported within 'the envelope by means of an insulating member 24,which is of a suitable material such as mica.

A plurality of pins 26 extend through the header 14. The pins 26 serveto support the member 24 within the envelope 16 and also serve aselectrical leads for the electrodes of the cage assembly. Suitablemembers 28 connect the .pins 26 to the various electrodes of the cageassembly 16.

In FIG. 1, the cathode assembly 22 is shown in its preferred'embodiment.The cathode assembly 22 comprises an inner tubular member 30 and anouter tubular member 32. T he'tubular members 30 and 32 are spaced romeach other and are, preferably, in the form of spaced concentriccylindrical tubes; although, it is obvious that configurations otherthan circular may be utilized. The inner tube Si) is preferably of a lowheat conducting material such as Inconel, an International NickelCompany trademark for a high nickel-chromium alloy including about 79.5%nickel, 13% chromium, 6.5% iron, and lesser amounts of manganese,silicon, carbon and copper. The outer tube 32 is made of a suitablematerial such as nickel. The tubular members 30 and 32 are maintained ina spaced relationship with the. outer member being supported by theinner member through the utilization of a washer or apertured'disk 36which is positioned between thetwo members 30 and 32 at their upperedge. The disk 36 is retained in position by welding it to the innermember'3l) and outer member 32 along itsinnerand outer peripheries toform a unitary structure. It is seen that the washer 36 not only spacesthe two tubular members 30 and 3 2, but also acts as ameans forsupporting the outer member 32 from the inner tubular member 30. Thewasher 36 also closes olf the end space between the two tubular members30 and 32 and prevents, in this area, the loss 'of heat throughradiation from the heater. The washer 36 is preferably made of a goodheat conducting material, for example, nickel. Thus, it is seen that agood heat conducting path is provided between the inner tube 30 araaoosand the outer tube 32, in order to raise the temperature of the outertube 32.

A heater assembly 33 is positoned within the space between the twotubular members 3% and 32 to provide for the heating of the cathode. Theheater is generally or" standard construction and includes a length ofwire having an insulating coating on the outside thereof. In FIG. 1, theheater 38 is shown in the form of a coil which extends throghout thespace between the two tubular elemeans 30 and 32. A suitable electronemissive coating 34, which may be any or those known in the art, isplaced on the outside surface of the outer tubular member 32 to providefor electron emission upon the heating of the cathode.

A substantially disk-shaped support 24, of suitable material such asmica, glass or ceramic, is provided at the opposite end of the tubularmembers from the washer 36.

lsshown in FIG. 1, the shield 24 contains a centrally located aperture46 having a diameter equal to that of the inside diameter of the innertube 3%). The inner tube 39 may be provided at its lower end with aradially extending shield 44 which abuts against the 'upper surface ofthe support'zd. The shield 44 may be made integrally with the inner tube30.

The cathode assembly 22 is connected to the support 24 by means of arivet member 42 having a head 43 and a body portion 41. The body portion41 is of such size so as to provide a compression or force fit withinthe inside of the tubular member 30 with the head 43 of the rivet 42hearing against the lower surface of the support 24. The rivet member 42is preferably made of a poor heat conducting material such as lnconel soas to provide a poor heat conducting path to the support 24 and therebyminimize heat loss. a

As shown in FIG. 1, the outer tube 32 is slightly shorter in length thanthe inner tube 3! Thus, it is readily seen that while the inner tube 30contacts the shield 44, the outer tubular member 32 does not but isinstead positioned slightly apart therefrom. Thus, no direct conductivepath is provided in this area for the removal of heat from the outertube 32. The distance between lower edge 33 of the outer tube 32 to thetop surface of the shield 44 is somewhat critical. If this distance istoo large, heat will be lost from the spacing between the tubularmembers by radiation. If the space is too small, heat will be lostthrough radiation-conduction. .In practice, it has been found that adistance of from about to about mils produces good results.

In FIG. 2 and 3 there are shown modifications of the cathode structureof FIG. 1 in accordance with the present invention. FIG. 2 differs fromFIG. 1 primarily in that the washer 36 of FIG. 1 has been omitted and inits place has been substituted a flange portion 50. The flange portion59 is formed integrally with the inner tube and extends radiallyoutwardly therefrom such that it is in contact with the outer tube 32.The flange portion 56 and the outer tube 32 are then welded together attheir peripheral junction 51 to provide the requisite support for theouter tube 32 and the closure between the two tubular members. Also inFIG. 2, the means of securing the inner tube 30 to the shield 44 hasbeen changed. In this case, the shield 44 is afiixed to the inner tube30 through the use of a peripheral braze 54 on the upper surface of theshield 44. Also, it is noted that instead of the coil heater as in FIG.1, an expanded spade wound heater 37 has been utilized in thisembodiment.

FIG. 3 differs from FIG. 2 in that an inwardly extending flange 56 isprovided at the top portion of the outer tubular member 32. This flange56 extends radially inward and is in'contact with the inner tube 30.Again as in FIG. 2 a peripheral weld is made at the top edge of thetubes to provide the necessary closure and requisite support. The innertube 30 may be brazed to the cathode shield 44. A heater 39 of FIG. 3 isshown as an unfolded coil heater.

It is evident that any of the heaters shown, or any suit able heater,may be used in any of the embodiments and that the heater is providedwith leads extending through one or more holes within the member 24 toprovide the necessary power for the-heater.

In the preferred embodiment, the cathode is made with a ratio of overalllength to overall diameter of less than 2:1. This presents a morethickset cathode than is prevalent in the art. Thus, by the relativelylarge diameter and the means'for the prevention of heat loss, thecathode thus described is less susceptible to microphonics and is one ofhigh efficiency. The high efficiency primarily results from theconstruction of the cathode assembly which reduces, the radiation andconduction losses by incorporating, in the cathode design, heat shieldsand poor heat con- 'duction paths. Also, by the above-describedconstruction, it has been found that the temperature gradient along thecathode surface is very small. Thus, the emission qualities of thecathode of the present design are very'good.

While there have been shown and described what are at present consideredto be the preferred embodiments of the invention, modifications theretowill readily occur to those skilled in the art. For example, onepossible modification would utilize the support member 24 as the cathodeheat shield. It is not desired, therefore, that the invention be limitedto the specific arrangement shown and described and it is intended tocover in the appended claims all such modifications as fall within thetrue spirit and scope of the invention.

I claim as my invention:

1. An electron discharge device comprising an electrode cage assemblyincluding a thermionic cathode for the emission of electrons, saidcathode comprising a first tubular member, a second tubular member, saidfirst and second tubular members maintained in a substantiallyconcentric relation .to form a space between said tubular members,heater means disposed within said space said first tubular member being'made of a material having a higher heat conductivity than that ofsaid second tubular member, and means extending between said tubularmembers at one end thereof said means being made of a high heatconductive material to form an efiicient heat conducting path from saidsecond tubular member to said first tubular member.

2. An electron discharge device comprising an electrode cage assemblyincluding an electron emissive thermionic cathode, said. cathodecomprising inner and outer tubular members, said outer tubular membersbeing made of a material having a higher heat conductivity than thematerial of "said inner tubular member, said outer member beingpositioned around and spaced from said inner member, a heater disposedWithin the spacing betweensaid tubular members, an electron emissivecoating on the outer surface of said outer member, means at one end ofsaid tubular members for closing off the space between said members,said means formed as an annular'disc interposed between said tubularmembers andmade of a highly heat conductive material to establish a heatconducting path from said inner tubular member to said outer tubularmember, 'and shield means disposed at the opposite end of said membersand extending in a direction transverse to the axis thereof, said shieldmeans being secured to said inner member and being spaced with respectto the end of said outer member.

3. An electron discharge device comprising an electrode cage asesmblyincluding an electron emissive thermionic cathode comprising inner andouter spaced, hollow cylindrical members, said members being coaxial andsubstantially coextensive, said outer cylindrical member being made of ahigher heat conductivematerial than the material of said innercylindrical'member, an electron emissive coating on the outer surface ofsaid outer me. ber, heater means disposed between said members, discmeans atone end of said cylindrical members for closing off the spacetherebetween, said means having a radial dimension substantially smallerthan the axial dimensions of said cylindrical members and being made ofa highly heat conductive material to establish a heat conducting pathfrom said inner cylindrical member to said outer cylindrical member, andshield means disposed in a plane substantially perpendicular to .theaxis of said cylindrical members at the other end thereof, said shieldmeans extending across the spacing between said cylindrical members andbeing secured to said inner member and closely spaced from the end ofsaid outer member.

4. In an electron discharge device, an electron em-issive thermioniccathode comprising inner and outer spaced, hollow cylindrical members,said outer cylindrical member being made of a higher heat conductivematerial than the material of said inner cylindrical member, saidmembers being coaxial and substantially coextensive, an electronemissive coating on the outer surface of said outer member, heater meansdisposed between said members, means at one 'end of said cylindricalmembers for closing off the space therebetween, said means being formedof an annular disc member having a radial dimension substantiallysmaller than the axial length of said cylindrical members and being madeof nickel to establish an efi'icient heat path from said innercylindrical member to said outer cylindrical member, and shield meansdisposed in a plane substantially perpendicular to the axis of saidcylindrical member at the other end thereof, said shield means extendingacross the spacing between said cylindrical members and being secured tosaid inner member and closely spaced from the end of :said outer member,said spacing being in the range of from about 10 to 20 mils.

5. A thermionic cathode for the emission of electrons comprising a firsttubular member of relatively poor heat conduction material, a secondtubular member of relatively good heat conduct-ion material positionedabout and spaced from said first tubular member, heater means disposedwithin the space between said tubular members, means extending betweensaid tubular members at one end thereof whereby the space between saidtubular members is closed oif, and shield means disposed at the otherend of said tubular members, said shield means extending in a directiontransverse to the length of said tubular members and positioned in aclosely spaced relationship with respect to the end of said secondtubular member.

References Qited by the Examiner UNITED STATES PATENTS 1,955,537 4/34Davies 3l3339 2,650,997 9/53 Watfous 3l338 2,813,227 11/57 Sweet 31326OFOREIGN PATENTS 1,151,321 8/57 France.

DAVID J. GALVIN, Primary Examiner.

2. AN ELECTRON DISCHARGE DEVICE COMPRISING AN ELECTRODE CAGE ASSEMBLYINCLUDING AN ELECTRON EMISSIVE THERMIONIC CATHODE, SAID CATHODECOMPRISING INNER AND OUTER TUBULAR MEMBERS, SAID OUTER TUBULAR MEMBERSBEING MADE OF A MATERIAL HAVING A HIGHER HEAT CONDUCTIVITY THAN THEMATERIAL OF SAID INNER TUBULAR MEMBER, SAID OUTER MEMBER BEINGPOSITIONED AROUND AND SPACED FROM SAID INNER MEMBER, A HEATED DISPOSEDWITHIN THE SPACING BETWEEN SAID TUBULAR MEMBERS, AN ELECTRON COATING ONTHE OUTER SURFACE OF SAID OUTER MEMBER, MEANS AT ONE END OF SAID TUBULARMEMBERS FOR CLOSING OFF THE SPACE BETWEEN SAID MEMBERS, SAID MEANSFORMED AS AN ANNULAR DISC INTERPOSED BETWEEN SAID TUBULAR MEMBERS ANDMADE A HIGHLY HEAT CONDUCTIVE MATERIAL TO ESTABLISH A HEAT CONDUCTINGPATH FROM SAID INER TUBULAR MEMBER TO SAID OUTER TUBULAR MEMBER, ANDSHIELD MEANS DISPOSED AT THE OPPOSITE END OF SAID MEMBERS AND EXTENDINGIN A DIRECTION TRANSVERSE TO THE AXIS THEREOF, SAID SHIELD MEANS BEINGSECURED TO SAID INNER MEMBER AND BEING SPACED WITH RESPECT TO THE END OFSAID OUTER MEMBER.